1. Field of Invention
The invention relates to an ink ejecting device, such as an ink-jet head of an ink-jet printer and, more specifically, to an ink ejecting device that effectively uses deformation of a piezoelectric actuator.
2. Description of Related Art
A piezoelectric ink ejecting mechanism has been conventionally proposed for a printhead. In the piezoelectric ink ejecting mechanism, a piezoelectric actuator deforms to change the volume of an ink chamber. Ink in the ink channel is ejected from a nozzle when the volume of the ink chamber is reduced, while ink is drawn into the ink channel when the volume of the ink chamber is increased. A plurality of such ink ejecting mechanisms are disposed adjacent to each other, and ink is selectively ejected from an ink ejecting mechanism at a particular position to form desired characters and images.
An ink-jet head using such a conventional piezoelectric ink ejecting mechanism is disclosed in U.S. patent application Publication No. 2001/0020968, which is incorporated herein by reference. FIG. 14 is an enlarged sectional view of a conventional piezoelectric ink-jet head as disclosed in that publication. The piezoelectric ink-jet head includes a cavity plate 100 formed by laminating piezoelectric sheets 110-140 and a piezoelectric actuator 200 formed by laminating thin metal plates 210-230. The cavity plate 100 is formed with a nozzle 150 open toward the outside, a pressure chamber 160 communicating with the nozzle 150, and a common ink chamber 120 that distributes ink from an ink source (not shown), through an ink supply hole 180, to the pressure chamber 160. The piezoelectric actuator 200 has a pressure generating portion 280 that applies pressure to the pressure chamber 160 for ink ejection.
The pressure generating portion 280 is defined between a drive electrode 240 and a common electrode 250 in a piezoelectric sheet 220 of the piezoelectric actuator 200, and is polarized in a direction from the drive electrode 240 toward the common electrode 250. When an electric field generated parallel to the polarization direction is applied to the pressure generating portion 280, the pressure generating portion 280 expands in a direction of the thickness of the piezoelectric actuator 200. The deformed piezoelectric actuator 200 reduces the volume of the pressure chamber 160 and pressurize the ink therein. As a result, an ink droplet is ejected from the nozzle 150 that communicates with the pressure chamber 160.
The pressure generating portion 280 expands toward the pressure chamber 160 as well as toward the opposite direction, which may cause a pressure loss. Due to such a pressure loss, a relatively high voltage is required for the pressure generating portion 280 to expand as required toward the pressure chamber 160, and thus the cost of a power supply system is increased.
Another problem arises when the piezoelectric ink-jet head is formed by stacking the piezoelectric actuator 200 made of piezoelectric ceramic and the cavity plate 100 made of metal. Because there is a big difference in the linear expansion coefficient between the piezoelectric ceramic and the metal, the piezoelectric actuator 200 and the cavity plate 100 are likely to bend at a different rate with temperature changes when they are bonded or used for printing. This may cause positional shifts of ink dots and degrade print quality.